Steve Skaglund walks across the rubble on the east side of Saturday's fatal mudslide near Oso, Wash., on Sunday, March 23, 2014. / Genna Martin, AP

by Doyle Rice, USA TODAY

by Doyle Rice, USA TODAY

"Extraordinary" precipitation over the past few weeks was a likely factor in the catastrophic landslide that has killed at least 14 people and left more than 100 missing in Snohomish County, Wash., according to meteorologist Cliff Mass of the University of Washington.

The cause of Saturday's slide is believed to be ground water saturation from the earlier heavy rainfall, authorities reported Sunday.

The area is no stranger to copious rainfall: "The location is found in the western Cascade foothills, an area of often very heavy precipitation produced by air being forced to move upward by the terrain," Mass wrote on his blog Monday.

How wet? Mass reports that the northern Cascades have been drenched with about a foot more rain than average over the past month. It's easily been the wettest spot in the entire western USA, most of which is plagued by drought.

Nearby Seattle -- with 7.71 inches of rain -- is having its third-wettest March on record, according to data from the National Weather Service. "Through March 21, Seattle was only 0.69 inches away from tying their wettest March on record, set in 1950," said Jonathan Erdman, senior meteorologist for weather.com.

In the area of the landslide, there were some "very wet conditions earlier in the week," Mass said, "with at least 3-5 inches" of rain.

"So we had a very wet month, topped off with very heavy precipitation earlier in the week," he wrote.

The area remains under a flash flood warning, according to the weather service: "Flooding is still occurring upstream of the slide and flash flooding is possible downstream from Oso to Arlington," the weather service reported.

A chance of rain or showers is forecast across the region for each of the next six days.